And so what? That was Kakashi's peak power level, the fact that he hasn't it anymore doesn't mean he had. If Sasuke was to lose Rinnegan and Rikudo chakra, would you forget about the power he showed with them?
1. Can Kakashi Kamui someone's chakra network even though he sees it behind Naruto's flesh? No. Can Kakashi Kamui Sasuke even though he sees him behind Susano? Nope.
2. Peak power level or not, thread title is "current" Sasuke, so taking Kakashi from a different time period is like saying Konohmaru beats Sasuke because at one point in time, Sasuke was weaker. Again, moot point, nor was it relevant as Kakashi is weaker since he can't choose what he focuses on in a y/z/x axis similar to why he can't focus on thin air. It's impossible, end of story.
3. No, but if someone else made this thread and it says "current", I wouldn't mention past characters considering how he wouldn't be "unstoppable" had Juubi Jin Hagromo been alive. Not that it matters, since Kakashi gets curb-stomped.